Problems statement: Numerous authors have used energetic to explain the ecological success of N-fixing plants. Legume biodiversity assessment, species dynamics, nitrogen fixation monitoring and environment impact assessment of these ecological events in Al-Hassa Oasis, Saudi Arabia are rare and need to be continuous and more frequent. Approach: Thus the objectives of this study were to analyze legume abundance within and outside Al-Hassa Oasis and relate it to the distribution of the different genera. Results: Thirty two legume plant species from 20 genera have been recorded within and outside the Oasis. The largest genera were Cassia (4 species), Indigofera (4) and Acacia (3). Annual herbs were the dominant growth form (34% of species recorded), followed by shrubs (28%), perennial herbs (19%) and trees (19%). Eighteen alien plant species were recorded (maybe an underestimated number). The nitrogen fixation of the legume plant species in Al-Hassa Oasis was estimated/analyzing the fixing potentiality of these species and nonfixing reference species (Panicum turgidum) using the 15 N natural abundance method. Species with great nitrogen fixing capacity in Al-Hassa include: Medicago sativa, Vicia faba, Vicia sativa, Melitotus indicus, Dolicus lablab, Melitotus alba and Cliforia ternate. The mean biological fixation contribution of most of the recorded legume plants were high, varying from 3.9% (Indigofera argentea) to 64.6% (Medicago sativa). Conclusion: Al-Hassa Oasis is richer than expected based on its location within the desert zone. This study confirms the importance of the Oasis for national flora conservation in the Kingdom. results showed a good potential for use of the 15 N natural abundance methodology for evaluating the nitrogen fixation ability of the legume plants under field conditions as well as for the estimation of %Ndfa.

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Carthamus oxyacantha is a widespread wild safflower species in Middle Eastern countries and northwestern India, including Kazakhstan, Turkmenistan and Uzbekistan and the Kingdom of Saudi Arabia. This study was conducted to evaluate and compare four C. oxyacantha ecotypes collected from different regions in the Kingdom of Saudi Arabia, Al-Hassa, Al-Kharaj, Najran and Al-Jouf. Analysis of variance showed significant effects of ecotype on physiological traits (number of heads per plant, heads diameter (cm), number of seeds per head, thousand seed weight (g) and seed color). The ecotypes also significantly differed in their moisture, crude fat, crude protein, crude fiber, ash and carbohydrates seeds contents. Moisture varied from 5.5 to 6.3%, crude fat varied from 25.3 to 27.3%, crude protein from 9.6 to12.4%, crude fiber varied from 14.6 to 17.9%, ash from 3.2 to 4.2% and carbohydrates varied from 37.3 to 39.3%. The main fatty acids of linoleic, oleic, palmitic and stearic acids composed 89.7-97.2% of the total fatty acids in all ecotypes. The sum of linoleic, oleic and palmitic acids fatty acids in seed oil ranged from 88.5 to 92.1%. The tested ecotypes also varied in their amino acid composition of seed proteins. The seeds were rich in four amino acids: Arginine, Glycine, Valine and Leucine. According to the results of the present study, the Saudi C. oxyacantha oil seeds can be a potential source of protein and energy supplements in livestock feed.